Internal combustion engines, including diesel engines, gaseous-fueled engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. These air pollutants may be composed of gaseous compounds, which may include nitrous oxides (NOx). Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of NOx emitted to the atmosphere from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
It has been established that a well-distributed flame having a low flame temperature can reduce NOx production to levels compliant with current emission regulations. One way to generate a well-distributed flame with a low flame temperature is to premix fuel and air to a predetermined lean fuel to air equivalence ratio. However, naturally-occurring pressure fluctuations within the turbine engine can be amplified during operation of the engine under these lean conditions. In fact, the amplification can be so severe that damage and/or failure of the turbine engine can occur.
One method that has been implemented by turbine engine manufacturers to provide lean fuel/air operational conditions within a turbine engine while minimizing the harmful vibrations generally associated with lean operation is described in U.S. Pat. No. 6,698,206 (the '206 patent) issued to Scarinci et al. on Mar. 2, 2004. The '206 patent describes a turbine engine having a primary combustion zone, a secondary combustion zone, and a tertiary combustion zone. Each of the combustion zones is supplied with premixed fuel and air by respective mixing ducts and a plurality of axially spaced-apart air injection apertures. These apertures reduce the magnitude of fluctuations in the lean fuel to air equivalence ratio of the fuel and air mixtures supplied into the mixing zones, thereby reducing the harmful vibrations.
Although the method described in the '206 patent may reduce some harmful vibrations associated with a low NOx-emitting turbine engine, it may be expensive and insufficient. In particular, the many apertures associated with each of the combustion zones described in the '206 patent may drive up the cost of the turbine engine. In addition, because the reduction of vibration within the turbine engine of the '206 patent does not rely upon strategic placement of the apertures according to acoustic tuning specific to the particular turbine engine, the reduction of vibration may be limited and, in some situations, insufficient.